The invention relates to a feed pump with a driven impeller which rotates in a pump casing and has, in each case, in its end faces a ring of guide blades delimiting blade chambers and in which the blade chambers have an inflow region and an outflow region for the medium to be fed, and with partially annular ducts which are arranged in the pump casing on both sides in the region of the guide blades and which, with the blade chambers, form feed chambers, an inlet duct opening into one feed chamber and the other feed chamber opening into an outlet duct, and the feed chambers being connected to one another in the region of the blade chambers.
Such feed pumps are often used for feeding fuel in a fuel tank of an automobile and are therefore known. When the impeller rotates, the guide blades transmit an angular momentum to the medium to be fed and generate in the feed chambers a circulation flow which runs transversely to the direction of movement of the guide blades. This circulation flow enters the impeller in the inflow regions of the blade chambers and leaves the impeller in the outflow regions of the blade chambers. The circulation flows run in opposition and are continued in the partially annular ducts. Since the feed chambers are connected at the blade chambers which are located opposite one another, the fed liquid passes from the inlet-side feed chamber into the outlet-side feed chamber. The feed chambers of the known feed pumps have, in each case, at least approximately circular cross sections. In a feed pump intended for generating a high feed pressure, the feed chambers are, as a rule, arranged on a particularly large radius. In order to generate a high feed volume, it is necessary, as a rule, for the feed chambers of the feed pump to have large cross sections.
A disadvantage of the known feed pump is that a feed pump having a different characteristic is required, in each case, for different media to be fed and for different intended feed volumes and feed pressures. If the feed pump is to be used as a fuel pump in an automobile, it is necessary, for example for diesel and gasoline engines and for different engine powers, to have feed pumps which are designed specifically for these purposes.
The problem on which the invention is based is to design a feed pump of the initially mentioned type, in such a way that it can be adapted to different characteristics with the least possible outlay.
This problem is solved, according to the invention, in that the profiles of mutually opposite blade chambers and/or of the inflow regions and of the outflow regions are designed asymmetrically to one another, in the case of at least some of the blade chambers, in order to generate an intended feed pump characteristic.
By virtue of the profile of the blade chambers, the transmission of angular momentum, taking place in the impeller, to the medium to be fed can be influenced in a particularly simple way. Owing to the invention, it is possible, by means of the feed pump, to generate different characteristics simply by exchanging or reversing the rotation of the impeller and, consequently, to adapt the feed pump to the respective areas of use and the media to be fed.
According to an advantageous development of the invention, the blade chambers can be provided with different profiles in a simple way, if the profiles of the inflow regions and of the outflow regions are formed, in each case, by a radius, and if the radii of the inflow regions and of the outflow regions differ from one another in length and/or in origin. In this case, the size of the individual radii and the arrangement of the origins of the radii depend on the intended characteristic and therefore on the size of the feed pump and on the material values of the medium to be fed. In order to avoid flow losses, the profile of the blade chambers can be smoothed in a transitional region between the inflow region and the outflow region.
For the overflow of the medium to be fed, a higher pressure must prevail in the inlet-side feed chamber than in the outlet-side feed chamber. According to another advantageous development of the invention, in the inlet-side feed chamber a particularly high angular momentum is transmitted to the medium to be fed, if the blade chambers of the inlet-side feed chamber have a smaller radius at their inflow regions than at their outflow regions. By virtue of this design, the flow transition from the inlet-side feed chamber to the outlet-side feed chamber is improved, as compared with the known feed pump. The feed pump thereby has particularly high efficiency.
According to another advantageous development of the invention, it is conducive to further improvement in the flow transition from the inlet-side feed chamber to the outlet-side feed chamber if the blade chambers of the outlet-side feed chamber have a smaller radius at their inflow regions than at their outflow regions.
According to another advantageous development of the invention, the medium to be fed overflows from the inlet-side feed chamber into the outlet-side feed chamber with particularly low loss if the origins of the radii of the blade chambers of the inlet-side feed chamber are arranged further inward in the axial direction of the impeller than the origins of the radii of the blade chambers of the outlet-side feed chamber.
Often, in order to feed fuel, a feed pump is used, in which the connection of mutually opposite blade chambers is arranged between the inflow regions and the outflow regions of the blade chambers. Such feed pumps are, as a rule, designated as side channel pumps. In this case, the intended characteristics can be generated in a simple way by leading the inflow region or the outflow region of one of the blade chambers into a blade chamber located axially opposite this blade chamber. In this case, the inflow regions or the outflow regions of the blade chambers form part of the profile of the blade chambers located axially opposite these blade chambers. This may be carried out either by means of radii of different size or by means of a different arrangement of the origins of the radii.
The feed pump according to the invention has a particularly high zero feed pressure if the inflow region of the blade chamber of the inlet-side feed chamber is led into the blade chamber of the outlet-side feed chamber. In this case, a part stream is deflected from the circulation flow in the inlet-side feed chamber into the outlet-side feed chamber by means of the profiles of the blade chambers. This results in a particularly low-loss transition of the flow from the inlet-side feed chamber into the outlet-side feed chamber.
According to another advantageous development of the invention, it is conducive to a further increase in the zero feed pressure if the outflow region of the blade chamber of the outlet-side feed chamber is led into the blade chamber of the inlet-side feed chamber.
According to another advantageous development of the invention, in the case of average delivery coefficients of more than 0.4, high values for the pressure coefficient can be achieved if the inflow region of the blade chamber of the outlet-side feed chamber is led into the blade chamber of the inlet-side feed chamber.
According to another advantageous development of the invention, it is conducive to a further increase in the pressure coefficient in the case of average delivery coefficients if the outflow region of the blade chamber of the inlet-side feed chamber is led into the blade chamber of the outlet-side feed chamber.
Tests have shown that, in the case of gasoline fuel as the medium to be fed, the feed pump according to the invention has particularly high efficiency if the end of the outflow region led into the respectively opposite blade chamber is at an axial distance a=.gamma.1/2 (ra-ri) ra/ri from the end of the inflow region, ra designating the outer radius and ri the inner radius of the ring of guide blades and .gamma. being in the range of between 0.02 and 0.16.
It is conducive to further improvement in the efficiency of the feed pump according to the invention if the guide blades ascend from the middle region of the impeller toward the end faces, as seen in the direction of rotation of the impeller.